As a conventional technology of this type, there is one disclosed in Patent Document 1. A hydraulic working machine according to this conventional technology is provided with working equipment comprised of a crusher or vibratory breaker, a hydraulic actuator for driving the working equipment, said hydraulic actuator being comprised of a crusher cylinder or breaker cylinder, and a variable displacement hydraulic pump for feeding pressure oil to actuate the hydraulic actuator. This hydraulic working machine is also provided with a directional control valve for controlling a flow of pressure oil to be fed from the variable displacement hydraulic pump to the hydraulic actuator, a control device for switchingly operating the directional control valve, a pilot pump for feeding a pilot pressure to switch the directional control valve, and a variable solenoid relief valve arranged between the directional control valve and the hydraulic actuator to specify a maximum circuit pressure.
On the other hand, a conventional relief control system, which is arranged on the above-mentioned hydraulic working machine to control the relief pressure of the variable solenoid relief valve, is provided with a pressure sensor for detecting a circuit pressure, an adjustment unit for performing an adjustment such that a circuit pressure to be outputted from the pressure sensor becomes equal to a pressure required by the hydraulic actuator for driving the desired working equipment, and a controller for outputting, responsive to a control signal outputted from the adjustment unit, a control signal to control the relief pressure of the variable solenoid relief valve. This conventional relief pressure control system is also provided with a display unit for displaying, responsive to display signals outputted from the controller, a relationship between the circuit pressure outputted from the pressure sensor and the pressure required by the hydraulic actuator, and a start instruction unit for instructing a start of control of the variable solenoid relief valve.
The working equipment comprised of the crusher or breaker is mounted, and this conventional relief pressure control system performs control of the relief pressure of the variable solenoid relief valve while actuating the working equipment.